There are a number of techniques currently in use for the molding of composite laminates into desired shapes. One technique for molding such materials into broad contoured surfaces (among other shapes) is known as "vacuum bagging". In such a process, composite laminates in an uncured or partially cured state are layed up on a rigid mold and are then covered with a flexible mold often referred to as a "vacuum bag". The vacuum bag is sealed around the periphery thereof to a peripheral portion of the rigid mold or supporting structure therefor and a negative pressure is applied to the interior of the cavity defined by the two molds. This causes the application of ambient pressure exteriorly of the flexible mold to be applied thereto and the underlying composite lay-up for conformance of the lay-up to the rigid mold as the composite is cured. Those skilled in the art will appreciate that the quality of the finished composite product will in large measure depend upon the quality of the seal between the flexible vacuum bag and the rigid mold.
The prior art is repleat with various techniques for sealing the vacuum bag to the rigid mold. One technique involves the use of adhesives or semi-adhesives such as zinc chromate putty as a sealant between the vacuum bag and rigid mold. The application of such sealants is very labor intensive, requiring the time consumming removal of old sealant and application of new sealant between molding operations, and is, therefore, not well adapated to automated techniques. Furthermore, such sealants may not be compatible with certain vacuum bag compositions without special primers which further contribute to the time consumed in, and the cost of the molding operation. Moreover, to a certain extent, such sealants are unreliable, requiring the utilization of electronic leak sensors to monitor potential leakage past the sealant into the mold cavity.
Mechanical fasteners such as ribbed or flanged zippers, adhesive tape, clamps and the like are also used to seal vacuum bags to rigid molds in composite molding operations. However, the use of such fasteners is, like the use of adhesives described hereinabove, very labor intensive, requiring extensive, time consuming manipulation of the bag by a mechanic with an attendant, significant risk of vacuum bag damage from such manipulation each time the molds are assembled and disassembled.
It will also be appreciated by those skilled in the art, that neither adhesive sealants nor mechanical clamps allow any sliding movement of the vacuum bag over the composite lay-up and/or the rigid mold. Such movement may, in certain cases, be desirable to enhance the conformance of the vacuum bag to the rigid mold and lay-up, thus avoiding bridging of discontinuities by the vacuum bag, and to minimize damage to the vacuum bag due to plastic deformation or rupture thereof.
Accordingly, a technique for sealing a vacuum bag to a rigid mold in a composite molding operation, which is reliable, less labor intensive then present techniques and which permits a certain amount of sliding movement between the vacuum bag and the composite lay-up or rigid mold periphery is desirable.